In a method of recognizing a form ID (form type) from an image of a form prepared by an image scanner or the like, in recent years, the number of types of recognizable forms is increased and the number of types of forms between which a layout of ruled lines is similar is increased. Accordingly, as one of methods for recognizing a form ID (form type) from an image of a form, for example, a method for extracting a form ID (candidate for form ID) of which the degree of similarity to an image of a form is high from among a large number of form IDs by roughly correlating line segments is known. In this type of recognition method, detailed identification processing by a candidate for the form ID extracted from among a large number of form IDs and a form to be recognized is performed. Therefore, as compared with a case where the detailed identification processing by all form IDs and the form to be recognized is performed, it becomes possible to reduce a processing load and shorten the processing time.
When the candidate for the form ID is extracted, a correlation of the form ID with the form to be recognized is performed based on a feature amount of a line segment pair in the form to which the form ID is imparted and a feature amount of a line segment pair in the form to be recognized. In the feature amount of the line segment pair, for example, a value representing a relationship between line segments and calculated based on a length of each line segment of the line segment pair and a positional relationship between the line segments is used. That is, in this type of form recognition method, in a case where the relationship between the line segments in the line segment pairs is similar, a correlation of the form ID with the form to be recognized is performed. A form ID with a large number of times in which the form ID is correlated with the form to be recognized by a correlation for each line segment pair is extracted as a candidate for the form ID of the form to be recognized.
As one of related technologies in a form recognition method, a technology for correcting distortion which occurs in a line segment in an image of a form to be recognized and performing recognition in a case where the distortion occurs is known.
Examples in technical fields of form recognition include Japanese Laid-open Patent Publication No. 7-282193 and Japanese Laid-open Patent Publication No. 2015-169978.